Variable speed escalators are known, an example of which is described in Elevator World, January 1994, pages 92 and 94. However, it appears that control thereof has thus far been limited to establishing a single predetermined speed for each installation, rather than varying the speed at a given installation, during normal use of the escalator.
In the past few decades, interest in conservation has led to a variety of schemes for saving energy in the movement of people within buildings. For instance, studies have been made of the possibility of saving energy by shutting an escalator off (allowing it to come to rest) whenever it is carrying no passengers. However, such studies show that the cost of restarting the escalator upon the presence of a passenger typically exceeds the savings which may result from being shut down for a short period of time. In any event, the studies determine that the savings resulting from shutting an escalator down have so far ranged from negative values (utilizing more energy than allowing the escalator to continuously run) to average savings that are so small as to not warrant the additional inconvenience to the passengers and expense to the building owners.